Wiki info about La-7B-20

A single-seat cantilever monoplane fighter with a closed cockpit and retractable landing gear with a tail wheel. The La-7 was the successor to the La-5FN.
Testing began on the experimental La-5 Benchmark 1944 in February 1944, and went into series production in May 1944 with the designation La-7.
The La-5 Benchmark 1944 underwent tests with three synchronized Berezina B-20 aviation cannons. These new cannons were large-caliber UB machine guns redesigned for use with 20 mm rounds, and were not yet in series production. They were very light (only 25 kg) but unreliable. For this reason, the test reports recommended series production of the plane with the same armament as was used on the La-5FN – two 20 mm Shpitalny-Vladimirov ShVAK cannons.
In October 1944, the B-20 cannons went into production at the Kovrov Ordnance Plant, and in January–February 1945, the La-7 underwent testing with them again. The in-flight firing results showed that the reliability of the cannons had improved, but was still lower than that of the ShVAK cannons. Nonetheless, a small batch of the fighters with three cannons (these were also called “three-pointers”) was produced in the winter of 1944–1945 on the No. 381 Aviation Plant in Moscow.
The La-7 was also tested with three experimental Shpitalny SH-20 cannons, but this cannon was never adequately tuned, so it failed to make its way into the series.
The plane contained the twin-row air-cooled 14-cylinder A.D. Shvetsov ASH-82FN radial engine with a maximum output of 1,850 hp.
Its firing armament consisted of three 20 mm synchronized Berezina B-20 cannons with 130 rounds each.
The plane's bomb complement consisted of two detachable wing-mounted DZ-40 locking bomb racks, each of which could carry bombs with a caliber of up to 100 kg. It mostly used the general-purpose air-dropped FAB-50 and FAB-100 bombs, along with the ZAB-50 and ZAB-100 incendiary bombs and the AO-50 and AO-25 fragmenting bombs.
Approximately 368 planes of this model were made. Further production was stopped owing to the unsatisfactory reliability of the B-20 cannons. However, combat pilots liked the “three-pointer” La-7 and, like the test pilots, did not complain about the weaponry's operation.